Arrangement for varying air-fuel ratio



May 2, 1961 w. D. PRESTON ARRANGEMENT FOR VARYING AIR-FUEL RATIO 2Sheets-Sheet 1 Filed Dec. 30, 1958 I2 i Compressed Fig.

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May 2, 1961 w. D. PRESTON ARRANGEMENT FOR VARYING AIR-FUEL RATIO 2Sheets-Sheet 2 Filed Dec. 50, 1958 Air- Fuel Ratio Fig. 5

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ATTORNEY United States Patent 6 ARRANGENIENT FOR VARYING AIR-FUEL RATIOWilliam D. Preston, Swarthmore, Pa., assignor to Sun Oil Company,Philadelphia, Pa., a corporation of New Jersey Filed Dec. 30, 1958, Ser.No. 783,925

4 Claims. (Cl. 261-72) This invention relates to internal combustionengines, and more particularly to a means for varying the ratio of airto fuel in the mixture fed to the cylinders of such engines.

It is rather desirable to be able to adjust or vary, from time to time,the air-fuel ratio in an internal combustion engine, this air-fuel ratiobeing known in common parlance as the richness or leanness of themixture. For example, at full throttle, the maximum power output of theengine may be obtained at one particular value of air-fuel ratio, whileat part throttle the maximum fuel economy (in miles per gallon) may beobtained at another, different value of air-fuel ratio; generally, themaximum power output will call for an air-fuel ratio considerably less(that is, a richer mixture) than that corresponding to the point ofmaximum fuel economy. It would be convenient if the engine could beadjusted, at diiferent times and as required or desired, for maximumpower output or for maximum fuel economy. Again, variations oradjustments of the air-fuel ratio might become necessary, in order tooptimize the operation, when the engine is operated at differentaltitudes, due to the variation in density of the air with altitude.Thus, the

, air-fuel ratio corresponding to say the point of maximum fuel economywould be different at sea level than at an elevation of 10,000 feet.There would be a similar difference (for dilferent altitudes orelevations) in air-fuel ratio, for maximum power output.

An object of this invention is to provide a novel arrangement forcontrolling and optimizing the performance of an internal combustionengine.

Another object is to provide a novel arrangement for varying theair-fuel ratio of the mixture fed to an internal combustion engine.

A further object is to perform the foregoing objects in.

a simple and eificient manner, necessitating only a minimum ofmodifications to a conventional internal combustion engine.

The objects of this invention are accomplished, briefly, in thefollowing manner: the carburetor of an internal combustion engine ismodified by providing a'conduit leading to the inside or interior of thefloat chamber thereof. By applying selectively subatmospheric,superatmospheric, or atmospheric pressure to this conduit, and hence tothe interior of the float chamber, the air-fuel ratio of the mixture fedto the engine from the carburetor may be adjusted or varied. Thesubatmospheric and super-atmospheric pressures may be obtained,respectively, from a source of vacuum and from a source of positivepressure. The application of a subatmospheric pressure or vacuum(negative pressure) to the float chamber results in a mixture that isleaner (higher air-fuel ratio) than that resulting from the applicationof atmospheric pressure, while the application of a super-atmosphericpressure or positive pressure to the float chamber results in a mixturethat is richer (lower air-fuel ratio) than that resulting from theapplication of atmospheric pressure.

A detailed description of the invention follows, taken in conjunctionwith the accompanying drawings, wherein:

Figure l is a diagrammatic illustration of an air-fuel ratio controlsystem according to this invention; and

Figures 2-5 are various curves useful in explaining the operation of theinvention.

Referring now to Figure 1, the float chamber portion of a carburetor foran internal combustion engine is illustrated schematically at 1. Thecarburetor itself operates in a conventional manner to feed a mixture ofair and fuel (such as gasoline) to an internal combustion engine (notshown). The float chamber *1 includes a fuel inlet pipe 2, through whichliquid fuel such as gasoline is pumped by means of a conventionalmechanical fuel pump (not shown), and an outlet orifice indicated at 3,by way of which the fuel flows from the float chamber 1 to the meteringjets of the carburetor. float chamber 1 controls or governs the level ofthe gasoline 5 in chamber 1 in such a way that the liquid level in thischamber is at all times maintained at a predetermined height.

In order to apply the arrangement of this invention in a practicalmanner to an internal combustion engine employing a carburetor, both ofthe vents which in a conventional carburetor transmit the air pressurefrom the downstream side of the air cleaner to the fuel in the floatchamber 1 are plugged. Also, a hole is drilled through the air hornassembly of the carburetor into the float chamber 1, this hole beingfitted with suitable tubing to provide a conduit 6 which thus leads tothe inside or interior of the float chamber. The conduit 6 opens intothe space above the fuel 5 in float chamber 1, that is, into the spacenormally unoccupied by fuel 5. The pressure applied to conduit 6 willtherefore be effective on the fuel (gasoline) 5 in float chamber 1.

For experimental purposes only, and in order to test the arrangement ofthis invention in a modern automobile, a four-barrel carburetor wasmodified in the manner now to be described. Both of the vents in theprimary system, which normally transmit the air pressure from thedownstream side of the air cleaner to the fuel in the primary floatchamber, were plugged. The passage in the primary float chamber, whichlinks the primary and secondary float chambers together, was plugged;this passage is slightly above the normal fuel level and is ordinarilyused to relieve excess fuel from either chamber,

if it becomes temporarily flooded. The fuel needle seat the air hornassembly of the carburetor into the primary float chamber, and this holewas fitted with one-eighth- 1 inch I.D. tubing, thus providing a conduitcorresponding to that denoted by 6 in Figure l. The modificationsdescribed in this paragraph, in elfect, change the carburetor from afour-barrel one to a two-barrel one, and bring the air-fuel ratio of themixture metered by the carburetor; completely under the control of anypressure brought to bear on the fuel (such as 5) in the primary floatchamber (such as 1) by means of the conduit (such as .6).

An arrangement is provided for applying an adjustable pressure toconduit 6, and thereby also to the inside of carburetor float chamber 1,the pressure applied to such conduit thus being brought to bear on thefuel 5 in float chamber 1. The arrangement now to be described permitsthe selective application of sub-atmospheric (negative pressure orvacuum), atmospheric, or super-atmospheric (positive pressure) pressureto conduit 6, audio;-

Patented May 2, 1961 thermore permits adjustment of the value of thesubatmospheric or super-atmospheric pressure so applied.

A branch conduit 7 is coupled to a suitable source of vacuum or negativepressure (that is, subatmospheric pressure), this branch conduit beingcoupled by way of a valve 8 to the main conduit 6. Valve 8 is arrangedfor manual operation, to couple at will the vacuum source to the conduit6, and also to adjust the value of the vacuum or negative(subatmospheric) pressure applied to conduit 6. The vacuum may beconveniently obtained from the vacuum side of the mechanical fuel pumpin the automobile, as indicated in Figure 1. If it is not convenient, orif for some reason the obtaining of the required negative pressure fromthe fuel pump is disadvantageous, a small, auxiliary vacuum pump may beutilized instead, taking its running power from the internal cornbustionengine.

A standard mercury manometer 9 is provided (one end of the U-tube beingcoupled to conduit 6 and the other end being open to the atmosphere), tomeasure the pressure applied to conduit 6 at any particular time. Aspreviously stated, such pressure may be either negative, or zero, orpositive, with respect to atmospheric pressure.

A branch conduit 10 is coupled to the main conduit 6, and is alsocoupled to the out side of a pressure regulator 11. The in side ofpressure regulator 11 is coupled through a valve 12 to a small bottle 13of compressed air. Bottle 13 comprises a source of positive orsuper-atmospheric pressure. By means of the manuallyoperated valve 12and the manually-operated pressure regulator 11, the positive orsuper-atmospheric pressure source may be coupled at will to the conduit6, and also, the value of the super-atmospheric or positive pressure socoupled or applied to conduit 6 may be adjusted. If desired, a smallauxiliary pressure pump driven by the internal combustion engine may beutilized instead of the compressed air bottle 13, as a source ofpositive or superatmospheric pressure.

By suitably adjusting the valves 8 and 12 and the pressure regulator 11,while observing manometer 9, it is possible to apply zero gauge pressure(that is, atmospheric pressure) to conduit 6, and thus also to theinterior of float chamber 1. Likewise, it may be seen that it ispossible to selectively apply various desired values of negative(subatmospheric or vacuum) pressure (obtained by way of branch 7 fromthe source of vacuum), or of positive (super-atmospheric) pressure(obtained from positive pressure source 13, by way of branch 10), to theconduit 6 and thereby also to carburetor float chamber 1. Obviously, thepressure being applied to conduit 6 at any particular time may be read(in inches of mercury, gauge) by means of manometer 9. It may bepossible to simplify the arrangement illustrated in Figure 1, bydesigning a single valve construction which can be employed to supplyeither negative, zero, or positive pressure to conduit 6, at will, andto adjust the value of the positive or negative pressure so supplied.

Figure 2 is a set of curves obtained experimentally, using the apparatusof this invention. These curves were obtained with the internalcombustion engine on a dynamometer test stand, and representfull-throttle and roadload conditions as legended, the speed being heldat 2150 r.p.m. (O rn.p.h.). A so-called Orsat Analyzer, which functionsto analyze the composition of the exhaust gas, was used to determine theair-fuel ratios delivered by the (experimental) carburetor, modified asdescribed previously. From the values of the volume composition of theexhaust gas constituents (oxygen, carbon dioxide, carbon monoxide), theair-fuel ratio can be determined.

From Figure 2, wherein the values along the horizontal axis representpressure in inches of mercury with respect to zero or atmosphericpressure, it may be noted that the air-fuel ratio goes down or decreases(that is, the mixture becomes richer) as the pressure applied to theconduit 6 and float chamber 1 increases positively from zero oratmospheric pressure. Conversely, the air-fuel ratio goes up orincreases (giving a leaner mixture) as the pressure applied to floatchamber 1 increases negatively from zero. The operation of thisinvention to vary the air-fuel ratio out of the carburetor does notdepend upon the validity or invalidity of any particular theory.However, one explanation of the above-described action is as follows.The positive pressure, transmitted to the fuel 5 in float chamber 1, mayactually force more fuel out of the float chamber into the main airstream, thus making the mixture richer. The negative pressure or vacuum,applied-to the fuel in the float chamber, may actually slow down theflow of fuel into the main air stream, making the mixture leaner.

It is desired to be pointed out that the conduit 6 is used only forpressure purposes, and no volume or flow of air is required. Therefore,only a -low-capacity vacuum source (or a small auxiliary vacuum pumpcapacity) and a small bottle of compressed air (or a lowcapacitypressure pump) are necessary.

Figure 3 is a curve illustrating the effect of air-fuel ratio on aninternal combustion engine, under full throttle conditions. This curveindicates that the best air-fuel ratio, as far as brake horsepower isconcerned, was 12:1 for a particular engine. The effect of air-fuelratio on the brake horsepower may clearly be seen, from this figure. Forthis curve, engine power output was measured directly as brake torque ona laboratory dynamometer test stand, the brake horsepower being computedby conventional methods. The air-fuel ratio was obtained from ananalysis of the exhaust gas, as in Figure 2.

Once the variable air-fuel ratio carburetor had been calibrated and thecurves of Figmre 2 obtained, the internal combustion engine wasinstalled in an automobile and road tests were made. Figure 4 is a curveillustrating the effect of air-fuel ratio on the time required to climba hill, under certain conditions. To make this plot, the air-fuel ratiois determined by noting (by means of manometer 9) the pressure appliedto float chamber 1, and then reading off the air-fuel ratio from theappropriate curve in Figure 2. In Figure 4, the time on the verticalaxis is the time required to climb 0.387 mile of 6% grade at fullthrottle in fourth gear, from a 30 mph. start. By this method, theoptimum air-fuel ratio was found to be 12.321.

Figure 5 is a curve illustrating the efiect of air-fuel ratio on theroad-load fuel economy at 50 mph, the data being obtained from actualroad tests, with the air-fuel ratios being obtained as in Figure 4. Theroadload fuel economy of the car can be improved somewhat by leanermixtures, which of course means a higher airfuel ratio. Such higherair-fuel ratios can be obtained (see Figure 2) by applying a negativepressure (vacuum) to the carburetor float chamber. The best reasonableairfuel ratio was found to be about 16:1, with about 17.5 m.p.g.available. This differs from the air-fuel ratio and the result in mpg.of the carburetor, as received from the manufacturer. As shown in Figure5, richer mixtures than 14:1 will result in a considerable waste offuel.

Summarizing, the curves in Figures 3, 4, and 5 clearly show thedesirability of having an easily adjustable airfuel ratio. A convenientarrangement for providing such an adjustable air-fuel ratio has beendisclosed, in accordance with this invention.

The invention claimed is:

1. In an internal combustion engine, a carburetor for feeding a mixtureof air and fuel to said engine, said carburetor including a floatchamber; a conduit leading to the inside of said chamber, andmanually-operable means for selectively applying a subatrnospheric, anatmospheric, or a super-atmospheric pressure to said conduit, thereby tomanually vary the effective pressure inside said chamber and thus tomanually vary also the air-fuel ratio of the mixture fed to said engine,at the will of the operator.

2., The combination set forth in claim 1, wherein said means includesmeans for manually adjusting the value of the subatmospheric orsuper-atmospheric pressure ap plied to said conduit, thereby to enablemanual variation of the air-fuel ratio of the mixture While theengine-is running.

3. In an internal combustion engine, a carburetor for feeding a mixtureof air and fuel to said engine, said carburetor including a floatchamber; a conduit leading to the inside of said chamber, a source ofsubatmospheric pressure, a source of super-atmospheric pressure, andmanually-operable means for coupling at will either'said first-named orsaid second-named source, or neither, to said conduit, thereby tomanually vary the effective pressure inside said chamber and thus tomanually vary also 6, the air-fuel ratio of the mixture fed to saidengine, at the will of the operator.

4. The combination set forth in claim 3, wherein said means includesmeans for manually adjusting the value of the subatmospheric orsuper-atmospheric pressure supplied from the respective source to saidconduit, thereby to enable manual variation of the air-fuel ratio of themixture while the engine is running.

References Cited in the file of this patent UNITED STATES PATENTSSterner June 17, 1958

